Hash.new: print a deprecation warning when receiving keyword arguments (#7828)

[Feature #19236]

In Ruby 3.3, `Hash.new` shall print a deprecation warning if keyword arguments
are passed instead of treating them as an implicit positional Hash.

This will allow to safely introduce a `capacity` keyword argument in 3.4

Co-authored-by: Jean Boussier <[email protected]>

1 files changed, 9 insertions, 5 deletions

diff --git a/hash.c b/hash.c
index 63a51f54c4..323e0ad512 100644
--- a/hash.c
+++ b/hash.c
@@ -1714,17 +1714,21 @@ set_proc_default(VALUE hash, VALUE proc)
 static VALUE
 rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
 {
-    VALUE ifnone;
-
     rb_hash_modify(hash);
+
     if (rb_block_given_p()) {
         rb_check_arity(argc, 0, 0);
-        ifnone = rb_block_proc();
-        SET_PROC_DEFAULT(hash, ifnone);
+        SET_PROC_DEFAULT(hash, rb_block_proc());
     }
     else {
         rb_check_arity(argc, 0, 1);
-        ifnone = argc == 0 ? Qnil : argv[0];
+
+        VALUE options, ifnone;
+        rb_scan_args(argc, argv, "01:", &ifnone, &options);
+        if (NIL_P(ifnone) && !NIL_P(options)) {
+            ifnone = options;
+            rb_warn_deprecated_to_remove("3.4", "Calling Hash.new with keyword arguments", "Hash.new({ key: value })");
+        }
         RHASH_SET_IFNONE(hash, ifnone);
     }